1. Field of the Invention
The present invention relates to a dryer apparatus for drying a pressed web. More specifically, the present invention relates to a dryer apparatus which includes a plurality of single tier dryer sections in which successive sections dry alternate sides of the web as the web is transferred between successive sections without any open draw.
2. Information Disclosure Statement
In the papermaking art, a formed web of paper is pressed in a press section in order to remove as much water as possible from the formed web. Subsequently, the pressed web is guided around a plurality of heated drying cylinders in order to remove remaining water from the web.
Preferably, alternate sides of the web are successively brought into direct contact with the heated surfaces of the drying cylinders as the web moves through the dryer apparatus. Such successive drying of alternate sides of the web tends to enhance the uniform drying characteristics of the resultant dried roll.
U.S. Pat. No. 4,934,067 to Skaugen et al teaches the aforementioned drying apparatus which also permits transfer of the web between successive drying sections without open draw of the web. Consequently, the apparatus disclosed in U.S. Pat. No. 4,934,067 enables the restrained drying of the web not only in the wet section of the dryer apparatus, but along the entire length of the dryer apparatus.
More particularly, because the web is constrained by the dryer felt during transit of the web around the dryer and because vacuum is applied to hold the web on the felt during movement around an intermediate roll, cross-machine directional shrinkage of the web during drying is inhibited.
Also, during the transfer of the web between successive dryer sections, vacuum means is used to restrain the web against such cross-machine directional shrinkage and to prevent cross-machine directional shrinkage that would occur in such a transfer if an open draw transfer were utilized.
Therefore, the aforementioned disclosure of U.S. Pat. No. 4,934,067 not only enabled enhanced runnability, but also provided improved resultant sheet quality because due to the sheet being restrained against cross-machine directional shrinkage, edge curl of the web was inhibited.
However, in certain applications, it has been discovered that the provision of intermediate vacuum rolls and the like are unnecessary provided means are supplied for diffusing boundary air following the felt adjacent to such intermediate rolls.
More particularly, the present invention provides a dryer apparatus having a plurality of single tier dryer sections in which successive sections dry alternate sides of the web, the web being transferred between successive sections without any open draw, and in which the web is guided between adjacent dryers by an intermediate roll defining a plurality of circumferential grooves for diffusing the aforementioned boundary air.
Therefore, it is a primary objective of the present invention to provide a dryer apparatus which provides a significant contribution to the art of drying a pressed web.
Another object of the present invention is the provision of a dryer apparatus including an intermediate roll which defines a plurality of circumferential grooves for diffusing boundary air following a dryer felt that would otherwise tend to lift the web from the felt extending around the intermediate roll.
Another object of the present invention is the provision of a dryer apparatus having an intermediate roll defining a plurality of grooves such that inherent machine directional shrinkage of the web during drying thereof inhibits cross-machine directional shrinkage of the web during movement of the web between successive dryers.
Another object of the present invention is the provision of a dryer apparatus in which each intermediate roll has a diameter which is substantially less than the diameter of adjacent dryers such that the machine directional shrinkage increases the tension of the web between successive dryers so that the pressure exerted by the web against the dryer felt during movement of the web around the intermediate roll is increased in conformity with an equation PS=TW/RI, where PS is the pressure exerted by the web on the felt, TW is the machine direction tension of the web, and RI is the radius of the intermediate roll.
Other objects and advantages of the present invention will be readily apparent to those skilled in the art by a consideration of the detailed description contained hereinafter taken in conjunction with the annexed drawings.